Generic diagnosis (after Baudin-Laurencin 1971, Petter 1979, and Pinto et al. 1988). Camallanidae. Body elongated, tapering at each end. Buccal capsule with two valves, marked internally by numerous interrupted ridges in both sexes. Mouth opening slit-like. Pair of tridents associated with buccal capsule. Oesophagus comprises an anterior muscular portion, and a posterior glandular portion of about equal length. Cuticle thin, finely striated in both sexes.
One species, O. melanocephala, is known from one fish species in Canada.